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Recent Results from KamLAND

Recent Results from KamLAND. R. D. McKeown Caltech. BNL – January 17, 2006. Outline. Historical Introduction Neutrino physics Neutrino mixing and oscillations KamLAND reactor neutrino results Geoneutrinos Future prospects. Discovery of the Neutrino – 1956.

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Recent Results from KamLAND

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  1. Recent Results from KamLAND R. D. McKeown Caltech BNL – January 17, 2006

  2. Outline • Historical Introduction Neutrino physics Neutrino mixing and oscillations • KamLAND reactor neutrino results • Geoneutrinos • Future prospects

  3. Discovery of the Neutrino – 1956 F. Reines, Nobel Lecture, 1995

  4. Subsequent History • 60’s and 70’s – n became the darling of accelerator-based particle physics ne≠ nm • 1968 – 1st solar n anomaly evidence • 1980’s – new interest in neutrino oscillations (F. Reines, …..) • 1980-present: the quest for neutrino oscillations • 1998 – evidence from Super-K

  5. Super-Kamiokande Results

  6. Two Generation Model 1.24 (Peg minimum)

  7. Missing solar neutrinos…

  8. n2 n1 Matter Enhanced Oscillation (MSW) Mikheyev, Smirnov, Wolfenstein

  9. Maki – Nakagawa – Sakata Matrix CP violation

  10. Pre – KamLAND summary • Persistent observations of deficit of solar neutrinos • 1998 – observation of oscillations of atmospheric neutrinos by Super-K • 2002 – SNO results imply matter-dependent oscillations of solar neutrinos Time to get our feet on the ground!!

  11. W.A. Fowler Nobel Lecture, 1983

  12. We need a “laboratory” Experiment!!

  13. Enter • Long Baseline (180 km) • Calibrated source(s) • Large detector (1 kton) • Deep underground (2700 mwe)

  14. Neutrino Oscillation Studies with Nuclear Reactors • ne from n-rich fission products • detection via inverse beta decay (ne+pge++n) • Measure flux and energy spectrum • Improve detectors, reduce background • Variety of distances L= 10-1000 m

  15. g 2.2 MeV d + p e n n g g 511keV 511keV Detection Signal Coincidence signal: detect • Prompt: e+ annihilation g En=Eprompt+En+0.8 MeV • Delayed: n capture 180 ms capture time

  16. The Reactor Neutrino Flux and Spectrum Reactor Isotopes ~ 200 MeV per fission ~ 6 e per fission ~ 2 x 1020e/GWth-sec • 235U, 239Pu, 241Pu from b measurements • 238U calculated • Time dependence due to fuel cycle

  17. Reactors are calibrated sources of n ’s !! Precise Measurements Flux and Energy Spectrum g ~1-2 %

  18. Negative Oscillation Searches 103 Distance (m)

  19. (From PDG) The BIG picture: SK atm (nmgnt)

  20. Kashiwazaki Takahama Ohi KamLAND uses the entire Japanese nuclear power industry as a long­baseline source

  21. Many reactors contribute to the antineutrino flux at KamLAND *Eν>3.4MeV (Eprompt>2.6MeV) Detailed power and fuel Composition calculation used From electrical power Japanese average fuel used

  22. A limited range of baselines contribute to the flux of reactor antineutrinos at Kamioka Korean reactors 3.4±0.3% Rest of the world +JP research reactors 1.1±0.5% Japanese spent fuel 0.04±0.02%

  23. Spectrum Distortion

  24. Front End Electronics Waveforms are recorded using Analog Transient Waveform Digitizers (ATWDs), allowing multi p.e. resolution Blue: raw data red: pedestal green: pedestal subtracted • The ATWDs are self launching with a threshold ~1/3 p.e. • Each PMT is connected to 2 ATWDs, reducing deadtime • Each ATWD has 3 gains (20, 4, 0.5), allowing a dynamic range of ~1mV to ~1V ADC counts (~120 mV) Samples (~1.5ns)

  25. The KamLAND Collaboration

  26. KamLAND:timeline • Summer 2000 PMT installation • Jun-Sept 2001 Fill Liquid Scintillator • Jan, 2002 Begin Data Taking • Dec, 2002 Report 1st Physics Results • Jun 2004 Report 2nd Reactor  Results • Sept 2005 Report geoneutrino evidence

  27. Energy Determination & Resolution DE/E ~ 6.2% /√E , Light Yield ~ 300p.e./MeV DEsyst = 2.0% at 2.6 MeV

  28. Tagged cosmogenics can be used for calibration τ=29.1ms Q=13.4MeV 12B 12N τ=15.9ms Q=17.3MeV μ Fit to data shows that 12B:12N ~ 100:1

  29. Energy calibration uses discrete γ and 12B/12N n-p n-12C 68Ge 60Co 65Zn Carefully include Birks law, Cherenkov and light absorption/optics to obtain constants for γ and e–type depositions σ/E ~ 6.2% at 1MeV

  30. Vertexing is performed using timing from the 17” PMTs -60 (2.6MeV) Am/Be(~8MeV) -65 (1.1MeV) -68 (1.0MeV) z

  31. Fraction of volume inside the fiducial radius verified using μ-produced 12B/12N and n (assumed uniform) 12B/12N neutrons

  32. Estimate of total volume and fiducial fraction

  33. Singles Background Source:Measured:Predicted 14C:? 210Pb: 102Hz:-- High Energy (e.g. μ): 0.33Hz:0.33Hz 85Kr: 606 Hz:-- 40K:1.9Hz:2.1Hz 208Tl: 3.2Hz:1.4Hz 232Th, cosmogenic: 0.19Hz

  34. Radioactivity inside Liquid Scintillator

  35. Selecting antineutrinos, Eprompt>2.6MeV 5.5 m fiducial cut • - Rprompt, delayed < 5.5 m • - ΔRe-n < 2 m • - 0.5 μs < ΔTe-n < 1 ms • 1.8 MeV < Edelayed < 2.6 MeV • 2.6 MeV < Eprompt < 8.5 MeV • Tagging efficiency 89.8% (543.7 ton) Balloon edge • …In addition: • 2s veto for showering/bad μ • 2s veto in a R = 3m tube along track • Dead-time 9.7%

  36. 99.998% CL Observed Event Rates 2002-4 dataset 766.3 ton•yr, Eprompt > 2.6 MeV Observed: 258 events No-oscillation: 365.2 ± 23.7 events Background 17.6 ± 7.2 events accidental 2.69 ± 0.02 9Li/8He (b, n) 4.8 ± 0.9 fast neutron < 0.89 13C(a,n) 10.0 ± 7.1

  37. Nobs – NBG Nno-osc =0.658 ± 0.044 (stat) ± 0.047 (syst) Evidence for Reactor ne Disappearance!! 99.998 % C.L.

  38. Solar n: Dm2 = 5.5x10-5 eV2 sin2 2Q = 0.833 G.Fogli et al., PR D66, 010001-406, (2002) Ratio of Measured and Expected ne Flux from Reactor Neutrino Experiments

  39. Oscillation Effect

  40. Time Variations of Reactor Power and Signals

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